In recent years, in electric motor control for a railway vehicle, an electrically driven automobile, etc., a desirable electric power control for the system is, in most case, performed by an inverter device using the large electric power semiconductor element.
In many cases, an intelligent power module (IPM) having an excessive temperature protecting function is used in the semiconductor element for large electric power used in such electric power control to prevent breakdown due to overheating. With respect to the excessive temperature protecting function of this IPM, for example, as shown in JP-A-2004-96318 (patent literature 1), there is a structure having a temperature detector and a switching speed variable circuit. The temperature detector detects the temperature of the vicinity of an IGBT chip of the semiconductor element for large electric power, and a diode chip. The switching speed variable circuit changes a switching speed in accordance with this temperature with respect to each of the above chips. When the temperature of each of the above chips exceeds a predetermined level, the switching speed of the chip is changed to prevent an excessive rise in temperature.
FIG. 10 shows one example of an internal structural view of the above intelligent power module (IPM). In this figure, an IGBT chip, a diode chip 21 and a temperature sensor 22 are arranged on an insulating substrate 20, and this insulating substrate 20 is arranged on a base plate 23. On the other hand, a control substrate 24 is arranged above the insulating substrate 20, and a gate drive circuit 25 required in switching of IGBT is mounted to this control substrate 24. The outer circumference of all these parts is covered with a case 26. A main circuit terminal 27 for flowing an electric current to IGBT and the diode, and a control circuit terminal 28 for transmitting a control signal required in the switching of IGBT are set to a structure guided from the above case 26 to the exterior.
As can be seen from the above structure, in IPM using the semiconductor element for large electric power, the temperature sensor 18 is arranged near IGBT and the diode chip, and junction temperatures of IGBT and the diode are presumed by detecting temperatures near the IGBT chip of the semiconductor element for large electric power and the diode chip. Accordingly, no junction temperatures of IGBT and the diode themselves are measured.
Patent literature 1: JP-A-2004-96318